Neotectonic indications in vicinity of a potentially active faults in the Sétif region (East )

Sahra AOURARI & Nadia Sidi Said CGS:Algerian Centre of Research Applied in Earthquake Engineering Located about 200 km from V The purpose of this presentation is to discuss the neotectonic indications around two faults assumed to be active in the Sétif region.

V choice has been focused on Sétif region because it crosses two distinct geological domains of the Maghrebides in Algeria, and therefore two distinct seismotectonic contexts: 1- The North of Sétif where a part of the Babors chain (external domain) with low to moderate but frequents seismic activity 2- The south of Setif where the high plains with low seismic activity. The presentation is structured in three parts:

ß first part : an introduction showing the geological overview the Northen domain in Algeria: Maghrébides chain,

ß second part: analysis of historical seismicity in Sétif region,

ß third part which is the subject of this presentation, is devoted to neotectonic investigations in vicinity of geological faults assumed to be active in Sétif region. Geological setting

Map of the main morphostructural domain of the North of Algeria ( redraw from Domzig, 2006).

V Sétif region (under red square) belongs to External zone of Maghrébides (Tellian chain). V Maghrébides are extending from to the Far East regrouping the peri- mediterrannean orogens. V Maghrébides are derived from opening then closure of the Tethys ocean basins system. V Since Upper Miocene, Pliocene, a number of Miocene network faults or reactivated older alpine faults are potentially actives Tectonic setting at regional scale:

VAllochthon of external zone regroups thrust sheet unites composed by of marls and lamestones of Jurassic- Cretaceous to Eocene. The para autochthon or High Plateaux domain characterized byTrias to Quaternay déposits.)

VPost nappe basins oriented E- W to ENE- WSW, are the spaces inherited from the alpine collision, characterized by Miocene,Pliocene and Quaternary diposits, and calco- alkaline magmatism.

VAlpine tectonic structures Simplified Structural schems of Eastern Algeria correspond mainly to NE-SW, [on basis of the geological map 1:200.000 - Kiken (1962] NW- SE system faults, E–W Thrust faults and NE-SW folds. Neotectonics takes place after the Alpine phases:

V upper Tortonian-Messinian, the littoral and intramountain basins. are the site of tectono-sedimentary events

VMiocene of the second cycle deposit

V Pliocene – Quaternary: continental sedimentation sometimes affected with brittle structures and occasionally pseudo- folds can be observed or detected. recent tectonics can be highlighted by reactivation of certain NE-SW reverse faults and E-W strike-slip faults in the Eastern Maghrébides. Second part: Historical Seismicity The Northern Algeria is a seismic domain due to its location close to the plates boundary. This domain includes: Tell Atlas with a high seismicity, High Plateaus with a very low seismicity, Atlas Saharian with a seismic activity.

The Eastern domain which Seismicity of the Ibéro-maghrébine (events [4-7] (Meghraoui, 2010) include Sétif seem less active than the central and western domains.

Seismotectonic map of the Algerian North showing the main active structures and its focal mechanisms (in Domzig, 2006). Babors seismotectonic setting

Babors chain (External zone of Maghrébides) localized between three department (Béjaia, , and Setif) is the most active where several earthquakes were recorded.

Premilary regional seismotectonic zonation Eastern Algeria (Tell and Tell Atlas) For the instrumental period, the number events recorded is relatively small and most recorded earthquakes are superficial and have low to moderate magnitudes. 4 earthquakes of maximum intensity VII EMS have been recorded. Seismicity map Historical Earthquakes described in Sétif area The seismic events compiled and listed (table ), it covering the period between 1860 and January 2010:

Before 1900 Période romaine Tremblement de terre (23Juillet 365) Séisme du 19 juillet 1867 Zone épicentrale : Eulma Epicentre macrosismique : 36.16°N, 5.68°E

Intensité du séisme I0= V (EMS) Since 1900… to present [from Harbi ,2010) séisme du 19 juillet 1924 Zone épicentrale :Tizi N’béchar[ les Babors de Sétif) séisme du 13 novembre 1957 Zone épicentrale : Sétif

Intensité maximale I0 = VI-VII EMS Séisme 18 février 1958 Zone épicentrale : Mahouan Epicentre microsismique : 36.20° N, 5.40° E

Intensité maximale I0= V-VI EMS Séisme du 4 septembre 1963 Zone épicentrale : Bir Hadada Intensité maximale est évaluée à VII-IX EMS Séisme du 2 mars 1967 Epicentre macrosismique : 36.18°N, 5.41°E

Intensité maximale I0 =V (EMS) Séisme du 26 septembre 1967 Zone épicentrale: El Mahdia

Intensité I0 =IV-V EMS (mais pas à , Khelil, Ras EL Ma, Sétif et Ain Abessa) Séisme du 27 janvier 1968 Zone épicentrale :Bir Hadada et Ras

I0 = V-VI EMS Séisme du 11 juillet 1975 Zone épicentrale : Ain Abessa-El Ourcia dégâts importantes des édifices publics ou habitations privées (80% des bâtisses endommagées)

Séismes 21 et 22 juin 1977 Zone épicentrale : Djemila Epicentre macrosismique : 36.29°N, 5.68°E

Intensité maximale :I0 = VI-VII EMS Le séisme du 10 novembre 2000 Zone épicentrale Beni-Ourtilane Epicentre macrosismique [36.71°N, 4.69°E (EMSC) ; 36. 434°N, 4.903°E (USGS)].

magnitude 5,7 I0 de VII MSK Depuis 2014 à présent Des secousses de faibles magnitudes enregistrées au Nord-Est de Sétif (Ben Aziz et Eulma) par le réseau sismologique algérien (CRAAG). Isoseismal maps of the main earthquakes [from Harbi ,2010) The seismicity map (diapo9)shows three classes of earthquakes; V(04 )earthquakes with magnitudes ≥5; VMore than 40 earthquakes ]4-5]; V (01) earthquake between ]3-4]; V earthquakes magnitude less than 3.

NB: many earthquakes are of undetermined magnitude

Seismotectonic map Active faults The Sétif region is marked by active and supposed active faults and actives faults which are all taken into account in the seismic hazard assessment studies: seismological fault [20 October 2000, Ms = 5.4 . fault responsible for many moderate earthquakes in the Babors of Setif and Bejaia. Third part : neotectonic investigations Remark:

ß Beni Ourtilane fault and Kharata fault observed in the maps(diapo 9, 11), are not the subject of this presentation)

ß We are interested to discribe the tectonic indications near the probable active faults:

V Djemila fault V Djebel Youcef fault Djebel Youcef fault Djemila fault Djemila Fault is a reverse fault oriented NE-SW. It puts in abnormal contact the Anté-Néogène (Djemila nappe) and Miocene. The activity of the fault can be indicated by the concentration of instrumental epicenters in the vicinity of the Djemila area. The map established by Vila (1980) reveals other NE-SW and E-W fault segments of significant length which can reach 35 km.

Djebel Youcef fault , would belong to the E-W alpine fault network. it limits the recent deposit to Cretaceous massif and it has 26 km in length The activity of this fault is suspected by the seismicity recorded at the anticline of Djebel Youcef. Obviousness related to the quaternary activity to the two faults Panoramic view of External domain in Sétif area : Tellian nappe “Straight" contact between the Miocene and the Quaternary marking the passage of a fault. Crétacé Crétacé

Miocène Terrasse1

Miocène Oued Menaa

Terrasse 2

Near Djemila : panoramic photo of Mena river

It is a rift zone that marks a neotectonic deformation zone; by a NNE-SSW fault ??

:. . Cretaceous strata (limestone and calcareous marl) inclined. It relates to the passage of the fault at the Oued Mena (N030)

Position : 0737781/40373471

Zoom Zoom

Fault NE-SW sub-vertical, are almost horizontal striation (lower than 10 °) L’Oued Ain Kebira (N300 ) presents a straight path

ENE WSW

Near the contact: Miocene postnappes almost vertical

Deposit: brown marls with remodeling cretaceous

Far from contact: Miocene post nappes is sub-horizontal Oued Dehamecha

at the intersection of Oued Ain Kebira (direction N300 ) with Oued Dehamecha Tributary river):

Under the bridge: fluviatile terraces suspended at different heights in a Cretaceous nappe. Three terraces: at 1m, 3m,> 3m l in relation to the current bed of the river)

. The disappearance of the Roman city Cuicul (Djemila) is really related to the earthquake (23Juillet 365) ??? Disappearance of Djemila city: the antique roman city following a catastrophe ??. The Roman city has disappeared for unknown reasons. It remained buried until its discovery following the archaeological excavations in the 50s

Djémila site known under its antique name Cuicul, is located 50 km NE of the town of Sétif and situated 900 m above sea-level. This antique site is an interesting example of Roman town planning adapted to a mountain location. It founded during the reign of (96 - 98 A.D); With its forum, temples, , triumphal arches and houses…etc Somes photos of the Djemila site Ain El Fouara Fountain Famous place South Sétif : In the plain

1- Djebel Youcef 2- High Plateau

Djebel Youcef anticline Strata: sub-horizonal

at the passage of the fault: Strata: straighten Titled stratum Fault plane in Miocene Plain Sétif Pliocene- Quaternary : horizonatal stratum Cretaceous

Scarp between Cretaceous massif and Quaternary plain

Quaternary

Cretaceous affected by alpine tectonics Recent fluviatile terraces in quaternary deposit

Fluvial terrace encrusted in Quaternary calcarenites Minimum three fluviatles terrasses encrusting the calcarenites

Plio-Quaternary deposits in the plain

Conclusion

Setif region is classified in the source zone "ZII" (seismic hazard); because it reveals indications of neotectonic activity.

The supposed active faults (Djemila Djebel Youcef), reveal in some places indications of recent activity.

Historical earthquakes recorded in Sétif region have induced maximum intensities of the order of VII in some places.

For the instrumental period, the number of recorded events is relatively significant. Seismicity is concentrated in the Babors. At least 4 earthquakes of maximum intensity VII EMS affected the region of Setif. Most recorded earthquakes are superficial and of low to moderate magnitude REFERENCE BIBBLIOGRAPHIQUE Ambraseys N.N. (1988). Engineering seismology. Earthquake Engineering and Structural Dynamics, 17, 1-105. Bouhadad Y., Nour A., Laouami N., Belhai D., (2003). The Beni-Ourtilane-Tachaouaft fault and Seismotectonic aspects of the Babors region (NE of Algeria). Journal of Seismology, 7 (1) 79-88. CGS (2003). Etude de l’aléa et microzonage sismiques de la ville de Constantine. Rapport interne, inédit CGS (2008). Etude de l’aléa sismique de la région de Constantine CGS (2009). Aléa sismique régional : --. Coutelle A. (1982). Géologie du Sud Est de la Grande Kbylie et des Babors d’Akbou. Thèse de doctorat, Univ. Pierre et Marie Curie , Paris VI , 567p. Domzig A. (2006). Déformation active et récente, et structuration tectonosédimentaire de la marge sous- marine algérienne. Thèse de Doctorat, université de Bretagne occidentale, 332p. Domzig A., Yelles A.K., Le Roy C., Déverchère J., Bouillin J.-P., Bracène R., Mercier de Lépinay B., Le Roy P., Calais E., Kherroubi A., Gaullier V., Savoye B. and Pauc H. (2006). Searching for the Africa-Eurasia Miocene boundary offshore western Algeria (MARADJA'03 cruise). C. R. Geoscience, 338, pp. 80-91. Durand Delga M. et Fontboté J.M. (1980). Le cadre structural de la Méditerranée occidentale. In Aubouin J., Debelmas J. et Latreille M (Eds.), Géologie des chaînes alpines issues de la Téthys, Colloque C5 du 26ème C.G.I., Mém. BRGM, 115, pp. 67- 85. Harbi. A (2001). -Analyse de la sismicité et mise en évidence d'accidents actifs dans le Nord-Est algérien. Thèse de Magister géophysique FASTGAT- USTHB, Alger. Harbi A., Maouche S. Benhallou H., (2003). Re-appraisal of seismicity and seismotectonics in the north-eastern Algeria Part II: 20th century seismicity and seismotectonics analysis. Journal of Seismology, 7 (2) 221-234. Harbi A., Maouche S. (2009). Les principaux séismes du Nord-Est de l’Algérie. Mémoires du Service Géologique National, Alger, 81 p. Kaabeche T. et Mebrak A. (2010). Contribution à l’étude des risques naturels (sismiques et mouvements de terrain) dans la Wilaya de Sétif. Mém. d’Ingénieur en Géologie Appliquée - Faculté des Sciences des Sciences de la Terre- Uni. Sétif Meghraoui M. (1988). Géologie des zones sismiques du nord de l'Algérie: tectonique active, paléoséismologie et synthèse sismotectonique. Thèse de Doctorat, université Orsay, Paris, 356 Rothé J.P. (1950). Les séismes de Kherrata et la séismicité de l’Algérie. Bull. Serv. Cart. Géol. Algérie, 4ème Série, Géophysique, n°3, 40 p.Vila J.M. (1977). Carte géologique détaillée de l’Algérie au 1/200.000, Sétif avec notice explicative détaillée (45 p.). Vila J.M. (1980). La chaîne alpine d'Algérie orientale et des confins algéro-tunisiens. Thèse de Doctorat, université de Pierre et Marie Curie Paris-VI, 3 vol., 663 p Thank you

Nadia Sahra